by Dr Justin Marley

Revising the Three Structure Model: Integration in Neuroscience: A Core Problem – Part 8

A Three Structure Model of Neural Activity in Relation to Consciousness and Language

In the last post I expended on the three model structure relating unconscious activity,conscious experience and language. In particular I looked at is how unconscious activity could be divided into absolute unconscious activity which would never reach conscious experience and transient unconscious activity which could. These changes are reflected in the diagram below.

How do these two types of unconscious activity that I’m proposing relate to language? A valid model would need practical applications and be able to say something useful about reality. Let us consider the example of the optic nerve. I have assumed that as one of the cranial nerves which conveys information to the visual cortex that it would be devoid of conscious experience. I don’t think this is too unreasonable. Now the question is how does absolute unconscious activity reach the stage of language? In the three structure model I have proposed that language would need to be preceded by conscious experience.

Intuitively we might suppose it is obvious that the information being transmitted from the eye via the optic nerve could be directly translated into language. However although there is processing in the retina before the information is transmitted down the optic nerve I am assuming that this is absolute unconscious activity. Therefore there has to be an indirect way for this activity to reach the stage of language. My suggestion is that this would occur by inference.

The reader may suppose that it is simple enough to demonstrate that activity in the retina leads directly to language describing this experience. For instance the simple act of opening one’s eyes in the morning allows the rays of sunshine to permeate the retinal layer. We might then say “it is very bright this morning”. Surely the activity in the retina has led directly to language? However the answer in this case is that it has not. Activity in the retinal layer is conveyed by the optic nerve to the visual cortex and also to other areas by the accessory optic tract. I would argue that it is in the visual cortex and visual association cortices where the conscious experience is occurring that precedes language.

However there is something quite curious that we need to explain. How is it that we can anticipate what the world will look like if one of our eyes is closed? We know intuitively that one part of the visual field will be obscured. I would argue that this is inference. We use our sensory apparatus almost continuously during wakefulness. We have developed through the course of our life a good understanding of what effects occur when we cover one eye, blink rapidly or look up suddenly. This understanding occurs through our conscious experience which is triangulated with a conscious experience occurring in the visual association cortex, visual cortex and associated areas.

The inferences that we make about the eye and its structures occurs in conscious experience and transient unconscious activity. If I close my eye I’m aware of the eye the eyelid and the surrounding structures. I know from past experience what will happen to my visual perception when I close the eye. When I close my eye my visual perception will alter. I’m combining direct conscious experience with a conscious experience based on inference about absolute unconscious activity. The direct conscious experience is exemplified by the statements

“the wall in front of me is a pale blue in colour”

The inference about absolute unconscious activity is exemplified by the statement

“I will no longer see the blue wall in front of me when I close my eyes”

The study of physiology may lead to an improvement in the inferences that we are able to draw in our conscious experience. We are in effect model building. The conscious experience of inference about our sensory apparatus is most likely distinct from our conscious experience of visual perception. Continuing with this compartmentalisation both these types of conscious experience are very distinct from the absolute unconscious activity occurring in the retina. We might distinguish between the experiential conscious experience of immediate visual perception and the more formalised conscious experience of inference.

The Anatomy of the Eye

Accommodation – The Role of the Lens

Refraction in the Eye

Accommodation – The Role of the Iris

A Little Speculation

All of this follows from the assumptions set out in the three structure model. There is room for a little speculation although in doing this the conclusions are much less firm and this is really an exercise in opening up new vistas. Firstly the conscious experience of visual perception and that of inference may be expected to occur in distinct brain areas. The conscious experience of visual perception may be expected to be closely linked to the emotional centres in brain. The reason I suggest this is that when we are experiencing a landscape for instance, we can be caught up in the moment and access our feelings in response to what we are seeing. There are some difficulties with this however. The visual cortex is located at the back of the brain whereas the Limbic structures (e.g Anterior Cingulate Cortex) and Insular Cortex are located much further forward. However the experience of being able to access emotions more easily with visual perception needs to be balanced by hard calculations. For instance we can calculate how many neuron relays there are between one location and another and then utilise this information together with the conduction velocities. placing too much reliance on the timing of conscious experiences during introspection is fraught with difficulty.

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